It is known that a capacitor can be produced in a semiconductor device. The capacitor produced in a semiconductor device is classified into two, including a stuck structure and a trench structure. The capacitor having the stuck structure is further classified into a thick film structure, a fin structure and a pipe structure. A capacitor having the pipe structure is assumed to be most promising in the near future. Since integration is one of the most important parameters for a semiconductor device, an increase in integration is naturally required for a capacitor produced in a semiconductor device.
A circuit in which a capacitor is connected in series with a field effect transistor is illustrated in FIGS. 1 and 2. FIG. 1 is a circuit diagram of the series circuit and FIG. 2 is the schematic cross section of a series circuit produced in a semiconductor device and in which a field effect transistor is connected in series with a capacitor having the pipe structure produced in a semiconductor device. The series circuit is frequently employed as a component of a dynamic random access memory having the one transistor and one capacitor structure. Referring to FIG. 1, an enhancement field effect transistor 1 is connected in series with a capacitor 2. Referring to FIG. 2, the field effect transistor 1 consists of a semiconductor substrate of one conductivity 1a, an element separation area 1b, a gate insulator layer 1c, a source (an area of the other conductivity) 1d, a drain (an area of the other conductivity) 1e, a gate electrode if and an insulator layer for covering the gate electrode 1g. The capacitor 2 consists of one electrode 2a which is a pipe having a closed bottom and which is made of conductive poly crystalline silicon, a dielectric layer 2b which is a layer of silicon dioxide covering the surface of the conductive poly crystalline silicon pipe 2a and the other electrode 2c which is made of conductive poly crystalline silicon to cover the surface of the dielectric layer 2b. A first connection line 3 made of conductive poly crystalline silicon is connected with the source 1d of the field effect transistor 1. This first connection line 3 is employed to connect the source 1d of the field effect transistor 1 with a bit line (not shown), in the case where the foregoing series circuit is employed as a component of the unit cell of a memory having the one transistor and one capacitor structure. The drain 1e of the field effect transistor 1 is connected with the one electrode 2a of the capacitor 2 by means of a connection piece 5 which penetrates an insulator layer 4 produced to cover the drain 1e. The other electrode 2c of the capacitor 2 horizontally extends from the capacitor 2 (To the right in the drawing). In the case of a memory having the one transistor and one capacitor structure, the other electrode 2c of the capacitor 2 is connected with the ground potential.
In order to increase the capacity of the foregoing capacitor having the pipe structure, it is effective to increase the surface area of the pipe. To increase the surface area of the pipe, the height thereof and/or the cross-sectional area of the pipe can be increased. However, an increase in the cross-sectional area of the pipe is accompanied by a decrease in integration, and an increase in height of the pipe is accompanied by a decrease in the mechanical strength of the pipe.